On the unsteady motion and stability of a heaving airfoil in ground effect

Molina, Juan Carlos; Zhang, Xin; Angland, David

doi:10.1007/s10409-011-0445-9

Cited by 16 publications

(8 citation statements)

References 27 publications

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“…Ellenrieder et al [11] explained the Strouhal number dependency of the wake vortex structure behind a translating airfoil. Meanwhile, many researchers investigated the RKVS in different situations, such as the wakes of fishes [12,13] in both experiments [14][15][16] and numerical simulations [16][17][18][19][20][21]. However, a clearly understanding of the transition mechanism between KVS and RKVS in the wake behind flapping foils was not available.…”

Section: Introductionmentioning

confidence: 99%

Numerical analysis on transitions and symmetry-breaking in the wake of a flapping foil

Wang

Zhang

et al. 2012

Acta Mech Sin

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Flying and marine animals often use flapping wings or tails to generate thrust. In this paper, we will use the simplest flapping model with a sinusoidal pitching motion over a range of frequency and amplitude to investigate the mechanism of thrust generation. Previous work focuses on the Karman vortex street and the reversed Karman vortex street but the transition between two states remains unknown. The present numerical simulation provides a complete scenario of flow patterns from the Karman vortex street to reversed Karman vortex street via aligned vortices and the ultimate state is the deflected Karman vortex street, as the parameters of flapping motions change. The results are in agreement with the previous experiment. We make further discussion on the relationship of the observed states with drag and thrust coefficients and explore the mechanism of enhanced thrust generation using flapping motions.

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Section: Introductionmentioning

confidence: 99%

Numerical analysis on transitions and symmetry-breaking in the wake of a flapping foil

Wang

Zhang

et al. 2012

Acta Mech Sin

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“…(13) and (14) to Eqs. (11) and (12) , respectively, we can obtain the velocity potentials in air and water induced by the rectangular vortex ring with incoming harmonic progressive water waves…”

Section: Green's Function For the Vortex Ring With Incoming Wavementioning

confidence: 99%

Nonlinear lifting theory for unsteady WIG in proximity to incident water waves. Part 2: Three-dimension

Liang

Zong

Zou

2013

Applied Ocean Research

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a b s t r a c tThe present article presents a nonlinear analysis for determining the three-dimensional unsteady potentialflow characteristics about a wing subject to wing-in-ground effect (WIG) operating above progressive water waves. By means of the time-domain Green's function for the three-dimensional dipole moving above the free surface satisfying the dynamic and kinematic boundary conditions on the mean free surface, the influence of the free surface on the vortex ring is considered. Then, the nonlinear unsteady lifting surface theory is developed to study the lifting problem for a three-dimensional wing operating above progressive water waves. Furthermore, the roll-up shed from the wing in the presence of a free surface and water waves is taken into account. With the computed results, the non-dimensional force coefficients (including the lift coefficient, induced drag coefficient and lift-to-drag ratio) are presented with the variation of different geometry and water wave parameters. The data reported in the literature are presented to validate the present approach.Crown

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“…The aerodynamic analysis of wings operating in ground effect has previously been conducted through both experimental and computational means . The computational studies [13][14][15][16][17][18][19][20][21][22][23] have, in general, used…”

Section: Introductionmentioning

confidence: 99%

Modelling boundary-layer transition on wings operating in ground effect at low Reynolds numbers

Roberts

Finnis

Knowles

2018

Proceedings of the Institution of Mechanical Engineers, Part D:

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The transition-sensitive, three-equation k- kL- ω eddy-viscosity closure model was used for simulations of three-dimensional, single-element and multi-element wing configurations operating in close proximity to the ground. The aim of the study was to understand whether the model correctly simulated the transitional phenomena that occurred in the low Reynolds number operating conditions and whether it offered an improvement over the classical fully turbulent k-ω shear stress transport model. This was accomplished by comparing the simulation results to experiments conducted in a 2.7 m × 1.7 m closed-return, three-quarter-open-jet wind tunnel. The model was capable of capturing the presence of a laminar separation bubble on the wing and predicted sectional forces and surface-flow structures generated by the wings in wind tunnel testing to within 2.5% in downforce and 4.1% in drag for a multi-element wing. It was found, however, that the model produced insufficient turbulent kinetic energy during shear-layer reattachment, predicted turbulent trailing-edge separation prematurely in areas of large adverse pressure gradients, and was found to be very sensitive to inlet turbulence quantities. Despite these deficiencies, the model gave results that were much closer to wind-tunnel tests than those given by the fully turbulent k-ω shear stress transport model, which tended to underestimate downforce. Significant differences between the transitional and fully turbulent models in terms of pressure field, wake thickness and turbulent kinetic energy production were found and highlighted the importance of using transitional models for wings operating at low Reynolds numbers in ground effect. The k- kL- ω model has been shown to be appropriate for the simulation of separation-induced transition on a three-dimensional wing operating in ground effect at low Reynolds number.

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On the unsteady motion and stability of a heaving airfoil in ground effect

Cited by 16 publications

References 27 publications

Numerical analysis on transitions and symmetry-breaking in the wake of a flapping foil

Numerical analysis on transitions and symmetry-breaking in the wake of a flapping foil

Nonlinear lifting theory for unsteady WIG in proximity to incident water waves. Part 2: Three-dimension

Modelling boundary-layer transition on wings operating in ground effect at low Reynolds numbers

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